Fish farming
Fish farming or pisciculture involves commercial breeding of fish, most often for food, in fish tanks or artificial enclosures such as fish ponds. It is a particular type of aquaculture, which is the controlled cultivation and harvesting of aquatic animals such as fish, crustaceans, molluscs and so on, in natural or pseudo-natural environments. A facility that releases juvenile fish into the wild for recreational fishing or to supplement a species' natural numbers is generally referred to as a fish hatchery. Worldwide, the most important fish species produced in fish farming are carp, catfish, salmon and tilapia.
Global demand is increasing for dietary fish protein, which has resulted in widespread overfishing in wild fisheries, resulting in significant decrease in fish stocks and even complete depletion in some regions. Fish farming allows establishment of artificial fish colonies that are provided with sufficient feeding, protection from natural predators and competitive threats, access to veterinarian service, and easier harvesting when needed, while being separate from and thus do not usually impact the sustainable yields of wild fish populations. While fish farming is practised worldwide, China alone provides 62% of the world's farmed fish production. As of 2016, more than 50% of seafood was produced by aquaculture. In the last three decades, aquaculture has been the main driver of the increase in fisheries and aquaculture production, with an average growth of 5.3 percent per year between 2000 and 2018, rising from 32.4 to 82.1 million tonnes.
Farming carnivorous fish such as salmon, however, does not always reduce pressure on wild fisheries, since such farmed fish are usually fed fishmeal and fish oil extracted from wild forage fish. Fish farming is a source of water pollution, and diseases and parasites can spread to wild populations. There are also fish welfare concerns related to overcrowding, which causes stress, injuries, and disease.
Although fish farming for food is the most widespread, another major fish farming industry provides living fish for the aquarium trade. The vast majority of freshwater fish in the aquarium trade originate from farms in Eastern and Southern Asia, eastern Europe, Florida and South America that use either indoor tank systems or outdoor pond systems, while farming of fish for the marine aquarium trade happens at a much smaller scale. In 2022 24% of fishers and fish farmers and 62% of workers in post-harvest sector were women.
Major species
| Species | Environment | Tonnage | Value |
| Grass carp | Freshwater | 5.23 | 6.69 |
| Silver carp | Freshwater | 4.59 | 6.13 |
| Common carp | Freshwater | 3.76 | 5.19 |
| Nile tilapia | Freshwater | 3.26 | 5.39 |
| Bighead carp | Freshwater | 2.90 | 3.72 |
| Catla | Freshwater | 2.76 | 5.49 |
| Crucian carp | Freshwater | 2.45 | 2.67 |
| Atlantic salmon | Marine | 2.07 | 10.10 |
| Roho labeo | Freshwater | 1.57 | 2.54 |
| Milkfish | Marine | 0.94 | 1.71 |
| Rainbow trout | 0.88 | 3.80 | |
| Wuchang bream | Freshwater | 0.71 | 1.16 |
| Black carp | Freshwater | 0.50 | 1.15 |
| Northern snakehead | Freshwater | 0.48 | 0.59 |
| Amur catfish | Freshwater | 0.41 | 0.55 |
Categories
makes use of local photosynthetic production or fish that are fed with external food supply.Extensive aquaculture
Extensive aquaculture relies on small or no external inputs of labour and feed, compared to what is being produced. The fish are usually kept in natural bodies of water or artificial ponds and are left to reproduce and feed without much intervention, surviving on the natural resources of where they are kept. This sort of aquaculture is the oldest, and most likely originated in China around 4000 years ago.Due to this type of aquaculture usually requiring large bodies of water, lakes and ponds may be converted to fish farms. This can pose a threat to local environments, both in terms of the habitats of local species being destroyed, and invasive species being introduced.
Intensive aquaculture
| Parameter | Optimal value |
| Acidity | pH 6–9 |
| Arsenic | < 440 μg/L |
| Alkalinity | > 20 mg/L |
| Aluminium | < 0.075 mg/L |
| Ammonia | < 0.02 mg/L |
| Cadmium | |
| Calcium | > 5 mg/L |
| Carbon dioxide | < 5–10 mg/L |
| Chloride | > 4.0 mg/L |
| Chlorine | < 0.003 mg/L |
| Copper | |
| Gas supersaturation | |
| Hydrogen sulfide | < 0.003 mg/L |
| Iron | < 0.1 mg/L |
| Lead | < 0.02 mg/L |
| Mercury | < 0.0002 mg/L |
| Nitrate | < 1.0 mg/L |
| Nitrite | < 0.1 mg/L |
| Oxygen | |
| Selenium | < 0.01 mg/L |
| Total dissolved solids | < 200 mg/L |
| Total suspended solids | < 80 NTU over ambient levels |
| Zinc | < 0.005 mg/L |
In these kinds of systems fish production per unit of surface can be increased at will, as long as sufficient oxygen, fresh water and food are provided. Because of the requirement of sufficient fresh water, a massive water purification system must be integrated in the fish farm. One way to achieve this is to combine hydroponic horticulture and water treatment, see below. The exception to this rule are cages which are placed in a river or sea, which supplements the fish crop with sufficient oxygenated water. Some environmentalists object to this practice.
Image:Abstreifen.JPG|thumbnail|left|250px|Expressing eggs from a female rainbow trout
The cost of inputs per unit of fish weight is higher than in extensive farming, especially because of the high cost of fish feed. It must contain a much higher level of protein than cattle feed and a balanced amino acid composition, as well. These higher protein-level requirements are a consequence of the higher feed efficiency of aquatic animals. Fish such as salmon have an FCR around 1.1 kg of feed per kg of salmon whereas chickens are in the 2.5 kg of feed per kg of chicken range. Fish do not use energy to keep warm, eliminating some carbohydrates and fats in the diet, required to provide this energy. This may be offset, though, by the lower land costs and the higher production which can be obtained due to the high level of input control.
Aeration of the water is essential, as fish need a sufficient oxygen level for growth. This is achieved by bubbling, cascade flow, or aqueous oxygen. Catfish in genus Clarias can breathe atmospheric air and can tolerate much higher levels of pollutants than trout or salmon, which makes aeration and water purification less necessary and makes Clarias species especially suited for intensive fish production. In some Clarias farms, about 10% of the water volume can consist of fish biomass.
The risk of infections by parasites such as fish lice, fungi, intestinal worms, bacteria, and protozoa is similar to that in animal husbandry, especially at high population densities. However, animal husbandry is a larger and more technologically mature area of human agriculture and has developed better solutions to pathogen problems. Intensive aquaculture has to provide adequate water quality levels to minimize stress on the fish. This requirement makes control of the pathogen problem more difficult. Intensive aquaculture requires tight monitoring and a high level of expertise of the fish farmer.
Very-high-intensity recycle aquaculture systems, where all the production parameters are controlled, are being used for high-value species. By recycling water, little is used per unit of production. However, the process has high capital and operating costs. The higher cost structures mean that RAS is economical only for high-value products, such as broodstock for egg production, fingerlings for net pen aquaculture operations, sturgeon production, research animals, and some special niche markets such as live fish.
Raising ornamental coldwater fish, although theoretically much more profitable due to the higher income per weight of fish produced, has been successfully carried out only in the 21st century. The increased incidences of dangerous viral diseases of koi carp, together with the high value of the fish, has led to initiatives in closed-system koi breeding and growing in a number of countries. Today, a few commercially successful intensive koi-growing facilities are operating in the UK, Germany, and Israel.
Some producers have adapted their intensive systems in an effort to provide consumers with fish that do not carry dormant forms of viruses and diseases.
In 2016, juvenile Nile tilapia were given a food containing dried Schizochytrium in place of fish oil. When compared to a control group raised on regular food, they exhibited higher weight gain and better food-to-growth conversion, plus their flesh was higher in healthy omega-3 fatty acids.
Fish farms
Within intensive and extensive aquaculture methods, numerous specific types of fish farms are used; each has benefits and applications unique to its design.Cage system
Fish cages are placed in lakes, bayous, ponds, rivers, or oceans to contain and protect fish until they can be harvested. The method is also called "off-shore cultivation" when the cages are placed in the sea. They can be constructed of a wide variety of components. Fish are stocked in cages, artificially fed, and harvested when they reach market size. A few advantages of fish farming with cages are that many types of waters can be used, many types of fish can be raised, and fish farming can co-exist with sport fishing and other water uses.File:Sustainable fish farming 010.jpg|thumb|Fish cages in Lake Victoria, Uganda
Cage farming of fishes in open seas is also gaining in popularity. Given concerns of disease, poaching, poor water quality, etc., generally pond systems are considered simpler to start and easier to manage. Also, the past occurrences of cage-failures leading to escapes, have raised concern regarding the culture of non-native fish species in dam or open-water cages. On August 22, 2017, there was a massive failure of such cages at a commercial fishery in Washington state in Puget Sound, leading to release of nearly 300,000 Atlantic salmon in non-native waters. This is believed to risk endangering the native Pacific salmon species.
Marine Scotland has kept records of caged fish escapes since 1999. They have recorded 357 fish escape incidents with 3,795,206 fish escaping into fresh and salt water. One company, Dawnfresh Farming Limited, has been responsible for 40 incidents and the escape of 152,790 rainbow trout into freshwater lochs.
Though the cage-industry has made numerous technological advances in cage construction in recent years, the risk of damage and escape due to storms is always a concern.
Semi-submersible marine technology is beginning to impact fish farming. In 2018, 1.5 million salmon are in the middle of a year-long trial at Ocean Farm 1 off the coast of Norway. The semi-submersible project is the world's first deep-sea aquaculture project, and includes -high by -diameter pen made from a series of mesh-wire frames and nets. It is designed to disperse wastes better than more conventional farms in sheltered coastal waters, therefore supporting higher fish packing density.
In Maritime Southeast Asia, traditional fish cages built around an offshore wooden platform are generally called kelong. They are usually used to temporarily keep caught fish until sold or cooked, but some are used for fish farming.